The journal of pharmacology and experimental therapeutics

Targeting PI3K/AKT/mTOR pathway in non small cell lung cancer.

Mammalian target of rapamycin (mTOR) regulates cell proliferation, autophagy, and apoptosis by participating in multiple signaling pathways in the body. Studies have shown that the mTOR signaling pathway is also associated with cancer, arthritis, insulin resistance, osteoporosis, and other diseases. The mTOR signaling pathway, which is often activated in tumors, not only regulates gene transcription and protein synthesis to regulate cell proliferation and immune cell differentiation but also plays an important role in tumor metabolism. Therefore, the mTOR signaling pathway is a hot target in anti-tumor therapy research. In recent years, a variety of newly discovered mTOR inhibitors have entered clinical studies, and a variety of drugs have been proven to have high activity in combination with mTOR inhibitors. The purpose of this review is to introduce the role of mTOR signaling pathway on apoptosis, autophagy, growth, and metabolism of tumor cells, and to introduce the research progress of mTOR inhibitors in the tumor field.

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mTOR signaling pathway and mTOR inhibitors in cancer: progress and challenges

PurposePhosphatidylinositol 3-kinase (PI3K) signaling is critical for the proliferation and survival of malignant B cells. Copanlisib, a pan-class I PI3K inhibitor with predominant activity against PI3K-α and -δ isoforms, has demonstrated efficacy and a manageable safety profile in patients with indolent lymphoma.Patients and MethodsIn this phase II study, 142 patients with relapsed or refractory indolent lymphoma after two or more lines of therapy were enrolled to receive copanlisib 60 mg intravenously on days 1, 8, and 15 of a 28-day cycle. The primary end point was objective response rate; secondary end points included duration of response, progression-free survival, and overall survival. In addition, safety and gene expression were evaluated.ResultsMedian age was 63 years (range, 25 to 82 years), and patients had received a median of three (range, two to nine) prior regimens. The objective response rate was 59% (84 of 142 patients); 12% of patients achieved a complete response. Median time to response...

Phosphatidylinositol 3-Kinase Inhibition by Copanlisib in Relapsed or Refractory Indolent Lymphoma.

Ras proteins are classical members of small GTPases that function as molecular switches by alternating between inactive GDP-bound and active GTP-bound states. Ras activation is regulated by guanine nucleotide exchange factors that catalyze the exchange of GDP by GTP, and inactivation is terminated by GTPase-activating proteins that accelerate the intrinsic GTP hydrolysis rate by orders of magnitude. In this review, we focus on data that have accumulated over the past few years pertaining to the conformational ensembles and the allosteric regulation of Ras proteins and their interpretation from our conformational landscape standpoint. The Ras ensemble embodies all states, including the ligand-bound conformations, the activated (or inactivated) allosteric modulated states, post-translationally modified states, mutational states, transition states, and nonfunctional states serving as a reservoir for emerging functions. The ensemble is shifted by distinct mutational events, cofactors, post-translational modifications, and different membrane compositions. A better understanding of Ras biology can contribute to therapeutic strategies.

Ras Conformational Ensembles, Allostery, and Signaling.

The pivotal roles of phosphatidylinositol 3-kinases (PI3Ks) in human cancers have inspired active development of small molecules to inhibit these lipid kinases. However, the first-generation pan-PI3K and dual-PI3K/mTOR inhibitors have encountered problems in clinical trials, with limited efficacies as a monotherapeutic agent as well as a relatively high rate of side effects. It is increasingly recognized that different PI3K isoforms play non-redundant roles in particular tumor types, which has prompted the development of isoform-selective inhibitors for pre-selected patients with the aim for improving efficacy while decreasing undesirable side effects. The success of PI3K isoform-selective inhibitors is represented by CAL101 (Idelalisib), a first-in-class PI3Kδ-selective small-molecule inhibitor that has been approved by the FDA for the treatment of chronic lymphocytic leukemia, indolent B-cell non-Hodgkin's lymphoma and relapsed small lymphocytic lymphoma. Inhibitors targeting other PI3K isoforms are also being extensively developed. This review focuses on the recent progress in development of PI3K isoform-selective inhibitors for cancer therapy. A deeper understanding of the action modes of novel PI3K isoform-selective inhibitors will provide valuable information to further validate the concept of targeting specific PI3K isoforms, while the identification of biomarkers to stratify patients who are likely to benefit from the therapy will be essential for the success of these agents.

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PI3K isoform-selective inhibitors: next-generation targeted cancer therapies

The phosphatidylinositol 3-kinase (PI3K) signaling pathway plays important roles in cell proliferation, growth, and survival. Hyperactivated PI3K is frequently found in a wide variety of human cancers, validating it as a promising target for cancer therapy. We determined the crystal structure of the human PI3Kα–PI103 complex to unravel molecular interactions. Based on the structure, substitution at the R1 position of the phenol portion of PI103 was demonstrated to improve binding affinity via forming a new H-bond with Lys802 at the bottom of the ATP catalytic site. Interestingly, the crystal structure of the PI3Kα–9d complex revealed that the flexibility of Lys802 can also induce additional space at the catalytic site for further modification. Thus, these crystal structures provide a molecular basis for the strong and specific interactions and demonstrate the important role of Lys802 in the design of novel PI3Kα inhibitors.

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Crystal Structures of PI3Kα Complexed with PI103 and Its Derivatives: New Directions for Inhibitors Design

Systematic combination screening reveals synergism between rapamycin and sunitinib against human lung cancer

Chronic lymphocytic leukemia (CLL) remains the most incurable leukemia. Early chemotherapeutic treatments, including alkylating agents, purine nucleoside derivatives, and immunotherapeutic antibodies, only show limited benefits for patients but severe off-target related side effects. Recent advances in understanding of the critical molecular pathways of regulating proliferation and survival of B-CLL cells have spurred a new therapeutical strategy by selectively targeting phosphoinositide 3-kinase delta (PI3Kδ). Idelalisib, a first-in-class PI3Kδ-selective small molecule has received the FDA's fast-track approval in July of 2014 as a new treatment of CLL, indolent B-cell non-Hodgkin's lymphoma, and relapsed small lymphocytic lymphoma. Undoubtedly, the success of idelalisib has provided a solid support in the development of PI3Kδ-specific inhibitors and reformed the concept of treating CLL. However, the number of reported selective inhibitors of PI3Kδ is very limited and very few have advanced into clinical trials. The mechanism of their actions remains elusive. More profound understanding on the modes of action of new PI3Kδ inhibitors will further validate the PI3Kδ-targeting strategy, and help to identify biomarkers capable of stratifying patients who will most likely benefit from the therapy.

Targeting PI3Kδ: emerging therapy for chronic lymphocytic leukemia and beyond.

mTOR inhibition led to activation of upstream receptor tyrosine kinases (RTKs) and AKT, which may attenuate the efficacy of mTOR kinase inhibitors. We sought to discover efficient drug combination with mTOR inhibitors by elucidating the survival feedback loops induced by mTOR inhibition in breast cancer. The feedback signaling upon treatment of mTOR inhibitor AZD8055 was determined and the combinatorial activity of AZD8055 and HSP90 inhibitor AUY922 in cell signaling and proliferation were detected. Treatment of breast cancer T47D cells with AZD8055 induced activation of AKT and phosphatidylinositol 3-kinase (PI3K), which was accompanied with increase in expression of multiple upstream proteins including EGFR, HER2, HER3 and IRS-1. Different RTKs were revealed to be responsible for the reactivation of AKT by AZD8055 in different breast cancer cell lines. Down-regulation of these proteins differentially enhanced the antiproliferative activity of AZD8055. AZD8055 and AUY922 displayed synergistic effect against a panel of human breast cancer cells irrespective their genotype, which was associated with enhanced cell cycle arrest and inhibition of DNA synthesis. AUY922 destabilized multiple tested tyrosine kinases and abrogated activation of AKT induced by AZD8055. AZD8055 also inhibited up-regulation of HSP70 and HSP27 upon AUY922 treatment. Cotreatment of these two drugs demonstrated synergistic activity against triple negative MDA-MB-468 xenograft without enhanced toxicity. The combination of AZD8055 and AUY922 demonstrated synergistic activity against various types of breast cancer and established a mechanistic rationale for a combination approach using catalytic mTOR kinase inhibitor and HSP90 inhibitor in the treatment of breast cancer.

Jian Ding

Papers

PI3K isoform-selective inhibitors: next-generation targeted cancer therapies

Crystal Structures of PI3Kα Complexed with PI103 and Its Derivatives: New Directions for Inhibitors Design

Systematic combination screening reveals synergism between rapamycin and sunitinib against human lung cancer

Targeting PI3Kδ: emerging therapy for chronic lymphocytic leukemia and beyond.

HSP90 inhibitor AUY922 abrogates up‐regulation of RTKs by mTOR inhibitor AZD8055 and potentiates its antiproliferative activity in human breast cancer